Blood Screening Trumps Biopsy in Cancer Mutation Hunt

April 6 (Bloomberg) -- A simple blood sample turned up
cancer-causing mutations more frequently than a tumor biopsy in
a study that suggests the approach could help deliver a clearer
picture of the disease and better tailor patients’ treatments.

In a study of Bayer AG’s drug Stivarga, researchers
analyzed tissue and blood samples from patients with
gastrointestinal stromal tumors, or GIST, to find cancer-driving
mutations. They found that blood samples were more likely to
reveal them than biopsies, in results presented today at the
American Association for Cancer Research meeting in Washington.

As cancer treatments increasingly home in on known genetic
causes of the disease, researchers need better tools to
determine just what mutations each patient has, said George
Demetri, director of the Ludwig Center at Dana-Farber Cancer
Institute and Harvard Medical School, who led the trial. Samples
taken from tumors may not reveal all the underlying mutations at
once, he said in an interview.

“A biopsy is by definition a subset of the tumor cells,”
Tyler Jacks, director of the Koch Institute for Integrative
Cancer Research at the Massachusetts Institute of Technology,
said in a telephone interview. He wasn’t associated with the
research. “What’s cool about this idea is the use of the blood
sample as a surrogate to what’s happening in the tumor.”

The screen, called BEAMing technology, is sensitive enough
to detect even rare mutations circulating in the blood stream in
the form of free DNA, genetic material shed from tumors. Demetri
said he expects the testing technology could become a standard
part of caring for cancer patients within five to 10 years.

Stivarga Trial

The analysis was done as part of Leverkusen, Germany-based
Bayer’s trial of Stivarga, a cancer therapy approved in February
for GIST and last year for colorectal cancer. Researchers took
DNA from tumor tissue and analyzed it for mutations in two genes
known to drive cancer-causing proteins targeted by Bayer’s drug
and medicines from Pfizer Inc. and Novartis AG, Sutent and
Gleevec.

Stivarga is approved for use in GIST after patients’ cancer
has stopped responding to Sutent and Gleevec. Bayer jointly
promotes Stivarga with Onyx Pharmaceuticals Inc. In the study,
researchers took blood samples from patients once their cancer
had progressed and analyzed them for mutations, including so-called secondary mutations that cause resistance to those drugs.

They found secondary mutations in 48 percent of blood
samples, versus 12 percent of tissue samples.

“The problem for the last decade of research is when you
take out one tumor and sample one corner of the tumor and then
sample another, you may see two different mutations in that same
tumor,” Demetri said in an interview. “What we were looking
for was technology that, with a simple blood test, we’d be able
to sample all the mutated DNA in a person’s body.”

Technology Limitations

The technology has some limitations, Demetri said. It
detects expected mutations, while is unable to turn up unknown
drivers of cancer. Newer versions of the technology are being
worked on now that would enable researchers to seek out
unidentified cancer-causing mutations, which could be helpful
for drug development.

The test may help identify which patients should receive
which drugs, Demetri said, enabling some to skip treatments that
won’t work for them or others to be given just the right therapy
for the driver of their cancer.

“Dynamic monitoring and understanding what’s happening to
the tumor over time, how it’s evolving, is important,” Jacks
said. “This technology allows you to do that.”